For many years, those who are responsible for monitoring usage of significant amounts of alternating current power have been concerned with the quality of such power. Much of the newer equipment now in use is sensitive to transient voltages, such as spikes, power surges, and random radio frequency (r.f.) noise; but at the same time, such equipment may be creating its own transient voltages which it injects back into the power line. When switches turn off and on, reverberating impulses are created on the line. Motors that start and stop cause power impulses known as surges.
Besides random r.f., pollution, electrical machinery of various kinds may generate harmonic frequencies. All of these kinds of power pollution detract from the efficiency of, inter alia, electric motors, generators, and transformers. The waveform of the power supplied to such equipment becomes distorted, resulting in the creation of eddy currents in the ferrous metal parts of such equipment, such as transformer cores and motor stators and rotors. The result is that eddy currents in a motor, for example, dissipate power as heat, thus causing the motor to consume more power to perform the same tasks. The motor may become damaged, either from the effect of excessive heat or from damage to insulation, causing it to break down long before its expected life.
While much has been done to improve that quality of the power being supplied to various consumers, there has been little recognition of the power pollution produced within a single facility as a result of the operation of significant numbers of electric motors, switches, computers, and other power-consuming devices.
Fundamentally, any time an inductive load is switched off, a very high voltage reverberation rising many times higher than the normal peak value of the applied voltage flows back into the power line. A typical transient voltage is shown superimposed on a sine wave in FIG. 1. It will be recognized that the result of the transient voltage is to cause peak voltages at a much higher value and frequency to distort the normal sine wave voltage. The average industrial or commercial circuit receives many daily transients in excess of 1000 volts. These transients reverberate and trigger other oscillations within the network. These reverberations bounce back and forth until they are absorbed or have done damage within the system.
Other disturbances occur when loads are unbalanced in three-phase lines, causing undesirable phase differences between voltage and current. High harmonic neutral currents flow, reacting with transient and surge activity on the line.
From the foregoing, it will be appreciated that the internal power pollution within a network frequently may be a much more serious factor in efficiency of motors, etc., than irregularities in the power supplied from outside the facility.
It has been estimated that up to 60 percent of all electricity is now, or soon will be, passing through non-linear loads. It is such loads that are principal contributors to electric power pollution.
Considerable efficiency gain can be realized if means can be provided that is connected to the individual power lines to such power-consuming units, which can absorb or otherwise remove such transient voltages, thereby preventing them from being injected back into the power line.
Further, in a digital logic control system, where binary bit patterns are used to implement control signals, random impulsive noise can knock out bits or put in bits where they should not exist. Thus, the control signal is altered and the desired action is lost. For this reason, it is important to inhibit the impulsive noise by clamping, filtering, and absorbing such noise before reaching the circuitry that will try to correlate the oncoming binary signal.
The present application constitutes a refinement and an extension of the teaching of U.S. Pat. No. 6,486,570 (common assignee) and describes different waveform correction filters useful with different applications.
It is, therefore, an object of the present invention to provide a waveform correction filter that removes and absorbs random r.f. noise, spikes, surges, and harmonics from the alternating current power supplied to the above-described power-consuming units.
It is another object of the present invention to provide a group of waveform correction filters that will substantially reduce maintenance costs for the associated equipment.
Other objects and advantages will appear from consideration of the following specification taken in connection with the drawings.